Power control circuit for sterilized devices, and associated systems and methods

ABSTRACT

A power control circuit for use with devices that will be placed in a flammable sterilizing gas includes a bi-stable switch that is configured to produce an output to place the circuitry of a connected device in a run state or a sleep state. The bi-stable switch controls one or more transistors to drain energy from energy storage devices in the circuitry of the connected device to a level below an ignition level of a sterilizing gas. A remotely actuatable switch can be actuated from outside of a packaging in which the power control circuit is placed to cause the bi-stable switch to produce an output that puts the circuitry in the run state without removing the power control circuit from the packaging.

TECHNICAL FIELD

The presently disclosed technology relates generally to electronic medical devices that are to be sterilized in flammable environments prior to use and, in particular, to sterilizable trial stimulators for use with implantable neurological stimulation systems.

BACKGROUND

Neurological stimulators have been developed to treat a variety of conditions such as pain, movement disorders, functional disorders, spasticity, cardiac disorders, and various other medical conditions. Implantable neurological stimulation systems generally have an implantable signal generator and one or more leads that deliver electrical pulses to neurological and/or muscle tissue. Often such devices have one or more electrodes that are inserted into the body near the target tissue to deliver the electrical pulses for therapeutic effect.

Once implanted, the signal generator is programmed to supply electrical pulses to the electrodes, which in turn modify the function of the patient's nervous system, such as by altering the patient's responsiveness to sensory stimuli and/or altering the patient's motor-circuit output. In spinal cord stimulation (SCS) therapy for the treatment of pain, the signal generator applies electrical pulses to the spinal cord via the electrodes that mask or otherwise alter the patient's sensation of pain.

In most cases, tests are performed to see if the patient notices an improvement from the application of the therapy pulses before a signal generator is implanted into the patient. Accordingly, an external trial stimulator is attached to the implanted electrodes and can be programmed to deliver electrical pulses with varying signal levels, frequencies, time durations etc. If the patient responds well after wearing the trial stimulator, the patient receives a more permanent implantable stimulator. The implantable stimulator can be programmed with the therapy regimen that was determined to be the most beneficial during the trial period. If necessary, the signal generator can be further programmed while implanted to fine tune the most beneficial therapy regimen.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a partially schematic illustration of an implantable spinal cord modulation system positioned at a patient's spine to deliver therapeutic signals in accordance with some embodiments of the present technology.

FIG. 2 illustrates a trial stimulator that is placed in a sterile package and that wirelessly communicates with a programming unit in accordance with some embodiments of the disclosed technology.

FIG. 3 is a block diagram of a power control circuit for selectively reducing stored energy in a trial stimulator to be sterilized in accordance with some embodiments of the disclosed technology.

FIG. 4 is a schematic diagram of a power control circuit for selectively reducing stored energy in a trial stimulator to be sterilized in accordance with some embodiments of the disclosed technology.

DETAILED DESCRIPTION

The present technology is directed generally to power control circuits for selectively powering circuit components and, in some embodiments for selectively powering circuit components in sterilizable devices, and associated systems and methods. In some embodiments, the presently disclosed technologies are directed to systems and devices for discharging energy storage elements in a medical device that is to be placed in a flammable sterilizing gas after manufacture and prior to use. For example, a bi-stable switch can control one or more transistors to drain energy from an energy storage device to a level below an ignition level of a sterilizing gas. The bistable switch can be triggered to change states via a remotely actuatable switch from outside a sealed packaging in which the circuit is placed so as not to break the sealed package in the process of re-activating the medical device.

Definitions

Unless otherwise stated, the terms “about” and “approximately” refer to values within 10% of a stated value.

As used herein, the term “and/or,” as in “A and/or B” refers to A alone, B alone and both A and B.

References to “some embodiments,” “one embodiment,” or the like, mean that the particular feature, function, structure or characteristic being described is included in at least one embodiment of the disclosed technology. Occurrences of such phrases in this specification do not necessarily all refer to the same embodiment. On the other hand, the embodiments referred to are not necessarily mutually exclusive. Elements described in the context of representative devices, systems and methods may be applied to other representative devices, systems and methods in a variety of suitable manners.

To the extent any materials incorporated herein by reference conflict with the present disclosure, the present disclosure controls.

As used herein, and unless otherwise noted, the terms “modulate,” “modulation,” “stimulate,” and “stimulation” refer generally to signals that have an inhibitory, excitatory, and/or other effect on a target neural population. Accordingly, a spinal cord “stimulator” can have an inhibitory effect on certain neural populations.

System Overview

FIG. 1 schematically illustrates a representative patient therapy system 100 for treating a patient's neurological disorders, arranged relative to the general anatomy of the patient's spinal column 191. The system 100 can include a signal generator 101 (e.g., an implanted or implantable pulse generator or IPG), which may be implanted subcutaneously within a patient 190 and coupled to one or more signal delivery elements or devices 110. The signal delivery elements or devices 110 may be implanted within the patient 190, at or off the patient's spinal cord midline 189. The signal delivery elements 110 carry features for delivering therapy to the patient 190 after implantation. The signal generator 101 can be connected directly to the signal delivery devices 110, or it can be coupled to the signal delivery devices 110 via a signal link, e.g., a lead extension 102. In some embodiments, the signal delivery devices 110 can include one or more elongated lead(s) or lead body or bodies 111 (identified individually as a first lead 111 a and a second lead 111 b). As used herein, the terms signal delivery device, signal delivery element, lead, and/or lead body include any of a number of suitable substrates and/or supporting members that carry electrodes/devices for providing therapy signals to the patient 190. For example, the lead or leads 111 can include one or more electrodes or electrical contacts that direct electrical signals into the patient's tissue, e.g., to provide for therapeutic relief. In some embodiments, the signal delivery elements 110 can include structures other than a lead body (e.g., a paddle) that also direct electrical signals and/or other types of signals to the patient 190, e.g., as disclosed in U.S. Patent Application Publication No. 2018/0256892, which is herein incorporated by reference in its entirety. For example, paddles may be more suitable for patients with spinal cord injuries that result in scarring or other tissue damage that impedes signal delivery from cylindrical leads.

In some embodiments, one signal delivery device may be implanted on one side of the spinal cord midline 189, and a second signal delivery device may be implanted on the other side of the spinal cord midline 189. For example, the first and second leads 111 a, 111 b shown in FIG. 1 may be positioned just off the spinal cord midline 189 (e.g., about 1 mm offset) in opposing lateral directions so that the two leads 111 a, 111 b are spaced apart from each other by about 2 mm. In some embodiments, the leads 111 may be implanted at a vertebral level ranging from, for example, about T4 to about T12. In some embodiments, one or more signal delivery devices can be implanted at other vertebral levels, e.g., as disclosed in U.S. Pat. No. 9,327,121, which is herein incorporated by reference in its entirety.

The signal generator 101 can provide signals (e.g., electrical signals) to the signal delivery elements 110 that excite and/or suppress target nerves. The signal generator 101 can include a machine-readable (e.g., computer-readable) or controller-readable medium (e.g. a memory circuit) containing instructions that are executable by a processor for generating suitable therapy signals. The signal generator 101 and/or other elements of the system 100 can include one or more processor(s) 107, memory unit(s) 108, and/or input/output device(s) 112. Accordingly, instructions for performing tasks such as providing modulation signals, setting battery charging and/or discharging parameters, and/or executing other associated functions can be stored on or in computer-readable media located at the signal generator 101 and/or other system components. Further, the signal generator 101 and/or other system components may include dedicated hardware for executing computer-executable instructions or configured logic circuitry such as FPGAs to perform any one or more methods, processes, and/or sub-processes described in the materials incorporated herein by reference. The dedicated hardware also serve as “means for” performing the methods, processes, and/or sub-processes described herein. The signal generator 101 can also include multiple portions, elements, and/or subsystems (e.g., for directing signals in accordance with multiple signal delivery parameters), carried in a single housing, as shown in FIG. 1, or in multiple housings.

The signal generator 101 can also receive and respond to an input signal received from one or more sources. The input signals can direct or influence the manner in which the therapy, charging, and/or process instructions are selected, executed, updated, and/or otherwise performed. The input signals can be received from one or more sensors (e.g., an input device 112 shown schematically in FIG. 1 for purposes of illustration) that are carried by the signal generator 101 and/or distributed outside the signal generator 101 (e.g., at other patient locations) while still communicating with the signal generator 101. The sensors and/or other input devices 112 can provide inputs that depend on or reflect a patient state (e.g., patient position, patient posture, and/or patient activity level), and/or inputs that are patient-independent (e.g., time). Still further details are included in U.S. Pat. No. 8,355,797, which is herein incorporated herein by reference in its entirety.

In some embodiments, the signal generator 101 and/or signal delivery devices 110 can obtain power to generate the therapy signals from an external power source 103. For example, the external power source 103 can by-pass an implanted signal generator and be used to generate a therapy signal directly at the signal delivery devices 110 (or via signal relay components). In some embodiments, the external power source 103 can transmit power to the implanted signal generator 101 and/or directly to the signal delivery devices 110 using electromagnetic induction (e.g., RF signals). For example, the external power source 103 can include an external coil 104 that communicates with a corresponding internal coil (not shown) within the implantable signal generator 101, signal delivery devices 110, and/or a power relay component (not shown). The external power source 103 can be portable for ease of use.

In some embodiments, the signal generator 101 can obtain the power to generate therapy signals from an internal power source, in addition to or in lieu of the external power source 103. For example, the implanted signal generator 101 can include a non-rechargeable battery or a rechargeable battery to provide such power. When the internal power source includes a rechargeable battery, the external power source 103 can be used to recharge the battery. The external power source 103 can in turn be recharged from a suitable power source (e.g., conventional wall power).

During at least some procedures, an external stimulator or trial stimulator 105 can be coupled to the signal delivery elements 110 during an initial procedure, prior to implanting the signal generator 101. For example, a practitioner (e.g., a physician and/or a company representative) can use the trial stimulator 105 to vary the modulation parameters provided to the signal delivery elements 110 in real time and select optimal or particularly efficacious parameters. These parameters can include the location from which the electrical signals are emitted, as well as the characteristics of the electrical signals provided to the signal delivery devices 110. In some embodiments, input is collected via the external stimulator or trial stimulator and can be used by the clinician to help determine what parameters to vary.

In a typical process, the practitioner uses a cable assembly 120 to temporarily connect the trial stimulator 105 to the signal delivery device 110. The practitioner can test the efficacy of the signal delivery devices 110 in an initial position. The practitioner can then disconnect the cable assembly 120 (e.g., at a connector 122), reposition the signal delivery devices 110, and reapply the electrical signals. This process can be performed iteratively until the practitioner determines the desired position for the signal delivery devices 110. Optionally, the practitioner may move the partially implanted signal delivery devices 110 without disconnecting the cable assembly 120. Furthermore, in some embodiments, the iterative process of repositioning the signal delivery devices 110 and/or varying the therapy parameters may not be performed.

The signal generator 101, the lead extension 102, the trial stimulator 105 and/or the connector 122 can each include a receiving element 109 or coupler that is configured to facilitate the coupling and decoupling procedure between the signal delivery devices 110, the lead extension 102, the pulse generator 101, the trial stimulator 105 and/or the connector 122. The receiving elements 109 can be at least generally similar in structure and function to those described in U.S. Patent Application Publication No. 2011/0071593, which is herein incorporated by reference in its entirety.

After the signal delivery elements 110 are implanted, the patient 190 can receive therapy via signals generated by the trial stimulator 105, generally for a limited period of time. During this time, the patient wears the cable assembly 120 and the trial stimulator 105 is secured outside the body. Assuming the trial therapy is effective or shows the promise of being effective, the practitioner then replaces the trial stimulator 105 with an implantable signal generator 101, and programs the signal generator 101 with therapy programs that are selected based on the experience gained during the trial period. Optionally, the practitioner can also replace the signal delivery elements 110. Once the implantable signal generator 101 has been positioned within the patient 190, the therapy programs provided by the signal generator 101 can still be updated remotely via a wireless physician's programmer 117 (e.g., a physician's laptop, a physician's remote or remote device, etc.) and/or a wireless patient programmer 106 (e.g., a patient's laptop, patient's remote or remote device, etc.). Generally, the patient 190 has control over fewer parameters than does the practitioner. For example, the capability of the patient programmer 106 may be limited to starting and/or stopping the signal generator 101, and/or adjusting the signal amplitude. The patient programmer 106 may be configured to accept inputs corresponding to pain relief, motor functioning and/or other variables, such as medication use. Accordingly, more generally, the present technology includes receiving patient feedback that is indicative of, or otherwise corresponds to, the patient's response to the signal. Feedback includes, but is not limited to, motor, sensory, and verbal feedback. In response to the patient feedback, one or more signal parameters can be adjusted, such as frequency, pulse width, amplitude or delivery location.

Sterilization

Because the trial stimulator 105 is connected to the signal delivery devices 110 within a sterile environment, the trial stimulator 105 must itself be sterile prior to use. As shown in FIG. 2, the trial stimulator is preferably stored in a sterile package 150 that is opened just prior to connecting the trial stimulator to the patient. In some embodiments, the sterile package 150 is a pouch that is permeable to sterilizing gasses but impermeable to microbe contaminants (e.g. bacteria, viruses, molds etc.). Suitable pouches are made from Tyvek® or other similar gas-permeable materials.

The most common type of gas used to sterilize medical devices is ethylene oxide (ETO). While this gas is effective for sterilizing equipment, it is also highly flammable. Ethylene oxide can ignite when exposed to an electrical energy discharge as low as 60 micro-joules. Care must be taken to ensure that any electrical circuitry placed in the packaging is completely or nearly completely discharged prior to exposure to the flammable sterilizing gas.

In addition, it is also beneficial if the trial stimulator 105 can be tested prior to its removal from the sterile packaging. Such testing can confirm the functionality of the unit prior to be being brought into a sterile operating theatre. In addition to or in lieu of testing, it may also be desirable to update the trial stimulator firmware and/or other software prior to removing the trial stimulator 105 from the packaging.

Given these implementation targets, an aspect of the presently disclosed technology includes a power control circuit that can be used with a trial stimulator to reduce the amount of energy stored in the trial stimulator to a level that allows the trial stimulator to be safely exposed to (e.g. placed in) a flammable sterilizing gas. In addition, the presently disclosed power control circuit can limit the battery drain of the trial stimulator while the trial stimulator is in a “sleep state” so that the battery remains sufficiently charged to power the circuit. In yet another aspect, the power control circuit can activate or awaken the trial stimulator while it is still in the sterile packaging. These and other aspects of the disclosed technology are discussed in further detail below. Although the power control circuit of the disclosed technology is described with respect to its use with a trial stimulator for nerve stimulation, it will be appreciated that the power control circuit can be used with other electronic devices that are to be stored prior to use and, in particular, with other electronic devices that are to be sterilized in a flammable gas environment.

FIG. 2 shows an environment in which a trial stimulator 105 is stored in a sterile packaging 150. Upon manufacture, the trial stimulator 105 is programmed with firmware required to control the internal circuitry used to deliver stimulation pulses to one or more electrodes in a patient. Once it is confirmed that the trial stimulator 105 is fully functional, it is placed in the packaging 150 and subjected to a sterilizing procedure. In some embodiments, the packaging 150 is a gas-permeable pouch (e.g. formed from Tyvek® or another suitable material) that allows a gas such as ethylene oxide to penetrate into the packaging and sterilize the trial stimulator 105 inside. The gas is withdrawn through the permeable material and the contents of the packaging 150 remains sterile as long as the packaging remains sealed.

Prior to use with a patient, the trial stimulator 105 in the sterile packaging 150 is awakened and begins to communicate with an external device such as a pulse programmer 160. Suitable modes of communication include short distance wireless communication protocols (e.g. Bluetooth, ZigBee, 802.11, infrared and/or other suitable protocols). In some embodiments, the trial stimulator 105 is awakened from a sleep state while still sealed in the sterile packaging 150. The trial stimulator 150 begins wirelessly communicating with the programmer 160 to confirm that the trial stimulator 105 is working and/or to confirm that a battery within the trial stimulator has sufficient power to operate the trial stimulator, and/or to update firmware and/or other stored parameters if necessary. Because the sterilizing gas has been removed from the packaging 150 prior to awakening the trial stimulator, there is no longer a risk of explosion if the trial stimulator is powered up. In some embodiments, the power control circuit draws minimal power from the battery so that the power control circuit is able to keep the trial stimulator in a sleep state for several years without draining the battery to the point that it cannot power the trial stimulator.

FIG. 3 is a block diagram of a power control circuit 200 configured in accordance with some embodiments of the disclosed technology. The power control circuit 200 includes a power source such as a battery 202 or other energy storage device (e.g. an energy storage capacitor). The battery voltage (V_(bat)) is connected to the trial stimulator circuitry 206 via an electronically controlled switch (e.g. a transistor) 204. The circuitry 206 includes, among other things, a processor, non-volatile memory for storing instructions or parameters, a radio transceiver for communicating with an external device and/or voltage regulators that produce higher voltages used to deliver the therapeutic pulses to the patient. In addition, the circuitry 206 may include energy storage devices (e.g. capacitors) that store energy in the trial stimulator.

In order to avoid storing enough energy in the trial stimulator to ignite a sterilizing gas, a bi-stable switch 220 controls one or more transistors 204, 222 to put the circuitry of the trial stimulator in a sleep state. In some embodiments, the bi-stable switch 220 puts the trial stimulator in a sleep state by turning off the transistor 204 so that power from the battery does not reach the circuitry 206 in the trial stimulator. In addition, any bus voltage levels and stored energy on the energy storage devices that could potentially ignite a sterilizing gas are drawn down to zero or near zero potential through one or more transistors 222.

In some embodiments, the bi-stable switch 220 operates as a flip flop circuit to produce an output that places the trial stimulator in a run state when battery power is first applied to the switch 220. A processor (not shown) within the trial stimulator circuitry 206 can provide a signal on a line 208 that causes the bi-stable switch 220 to change states and produce a signal that puts the trial stimulator in a sleep state. The signal on line 208 from the processor can be activated once a self-test routine is complete. Alternatively, the processor or other logic circuit can receive a command from an external programmer (not shown) via a wireless connection to put the trial stimulator in a sleep state.

A remotely actuatable switch 226 (e.g. a switch that is actuatable from outside the packaging 150 shown in FIG. 2) is provided to change the state of the bi-stable switch 220 and cause the bi-stable switch to produce a signal causing the connected circuitry to exit the sleep state and enter the run state. The switch 226 can be operated through the sterile packaging so that the trial stimulator need not be removed from the packaging in order to cause the trial stimulator to enter the run state. Suitable remotely actuatable switches include, but are not limited to, magnetically activated reed switches, mechanical switches, pressure activated switches, light activated switches, shock activated switches, and/or Hall-effect switches. In some embodiments, the switch 226 is mechanically operated so that it does not need to be powered while the trial stimulator is in the sleep state.

In some embodiments, the switch 226 is a magnetically activated reed switch. Placing a magnet on the outside of the sterile packaging near the switch 226 closes the reed switch and causes the power control circuit to produce an output that puts the trial stimulator in the run state. More particularly, closing the switch 226 causes the bi-stable switch 200 to generate an output that turns on the transistor 204 and applies the battery voltage to the circuitry 206 within the trial stimulator. In addition, closing the switch 226 turns off the transistor 222 and allows the energy storage devices in the trial stimulator to charge.

FIG. 4 is a schematic diagram of a representative embodiment of the power control circuit 200 shown in FIG. 3. The power control circuit 200 includes the bi-stable switch 220 that is configured as a JK flip flop. The flip flop includes two cross-connected FET transistors 250 and 254. Each of the first and second transistors 250, 254 has a source terminal that is grounded. The drain terminal of the first transistor 250 is connected through a first 10 MΩ resistor 258 to the battery voltage V_(bat). Similarly, the drain of the second transistor 254 is connected through a second 10 MΩ resistor 260 to the battery voltage V_(bat). The node between the drain terminal of the second transistor 254 and the second resistor 260 is connected through a first 1 MΩ resistor to the gate of the first transistor 250. Similarly, the node between the drain of the first transistor 250 and first resistor 258 is connected through a second 1 MΩ resistor to the gate of the second transistor 254. In this way, when the first transistor 250 is turned on, the second transistor 254 is held off. Conversely, when the second transistor 254 is turned on, the first transistor 250 is held off.

In the embodiment shown in FIG. 4, an output 262 of the flip flop circuit that is taken at the node between the drain of the second transistor 254 and the second resistor 260 drives a number of transistors that reduce the energy stored in a connected circuit when the circuit is in a sleep state. As shown, the output 262 feeds a gate of a p-type FET transistor 270 such that when the output 262 is a logic low level, the transistor 270 is turned on and connects the battery power to the connected circuitry 206. In addition, the output 262 is connected to gates of one or more n-type FET transistors 280 a, 280 b etc. When the output 262 is a logic low level, transistors 280 a, 280 b are turned off.

When the flip flop changes states, the output 262 goes to a logic high level and the transistor 270 is turned off, thereby disconnecting the battery power from the connected circuitry 206. In addition, the logic high level on output 262 turns the transistors 280 a, 280 b on. The transistors 280 a, 280 b are configured to connect any busses and any energy storage devices on the busses or other powered lines to ground through a 1 KΩ resistor so that their voltage is zero or near zero and the energy stored on the capacitors is less than an ignition energy level of a flammable sterilization gas. In some embodiments, the energy stored in the connected circuitry 206 while in the sleep state is reduced to less than 1/10th of that which could ignite a sterilizing gas (e.g. reduced to about 6 uJoules or less for ETO).

With the first transistor 250 conducting and the second transistor 254 in the non-conducting state, the connected circuitry 206 is put into a sleep state. The first and second transistors 250, 254 have a very low leakage current and the 10 MΩ) resistors in series with the drain electrodes limits the current of the conducting transistor in the sleep state to a low level (3.6V/10MΩ=360 nA) such that the battery drain is minimal during the sleep state.

In some embodiments, a first 1000 pF capacitor 264 is connected between the battery voltage and the gate of the second transistor 254. Similarly, a second 1000 pF capacitor 266 is connected to the gate of the first transistor 250 and ground. When battery power is first applied to the power control circuit, the first capacitor 264 acts as a short and the battery voltage appears at the gate of the second transistor 254 turning it on and producing a logic low level on the output 262 thereby placing the connected circuitry 206 in a run state. In this way, if a new battery is placed into the circuit, the connected circuitry 206 will immediately begin to operate in the run state. Capacitors 264, 266 also shunt stray EMF signals to ground or the battery and lessen the likelihood that any such EMF will change the state of the flip flop.

The power control circuit 200 will keep the connected circuitry operating in the run state until it is commanded to turn off. In some embodiments, an N-type FET transistor 290 has a drain connected to the gate of the second transistor 254. When the transistor 290 is turned on, the gate of the second transistor 254 is connected to ground and the second transistor 254 is turned off. The output 262 of the power control circuit then goes to a logic high level and the connected circuitry enters the sleep state. In some embodiments, a signal that controls the transistor 290 is received from a processor or other logic circuit in the connected circuitry 206, such that when the circuit completes a self-test or is commanded by an external controller, the processor puts a logic level on the gate of the transistor 290 to take the circuitry out of the run state and put it into the sleep state. A resistor/capacitor combination are connected to the gate of transistor 290 to de-bounce any jitters on the signal applied to the gate of transistor 290.

The power control circuit 200 will continue to produce an output to keep the connected circuitry in the sleep state until the flip flop changes states. In some embodiments, a remotely actuatable switch 300 such as a magnetically activated reed relay is connected between the battery voltage through a 10 KΩ resistor 292 and diode 294 to the gate of the second transistor 254. When the remotely actuatable switch 300 is closed, the battery voltage is applied to the gate of the transistor 254 thereby driving the output 262 to a logic low level and putting the connected circuitry 206 back in the run state. In some embodiments, a resistor divider is connected between the resistor 292 and the in-line diode 294 so that a processor or other logic circuit can detect whether the switch 300 is closed or open depending on the voltage level produced by the resistor divider.

The remotely actuatable switch 300 can be activated from outside of the sterile packaging so that the connected circuitry can be turned on without removing it from the packaging. As indicated above, other types of switches that can be activated through the sterile packaging could also be used such as pressure switches, shock activated switches, light activated switches or even mechanically controlled switches that can be activated through the packaging. A Hall effect switch can also be used, depending on the current draw required to remain powered.

As will be appreciated, the power control circuit 200 operates to selectively apply the battery voltage to connected circuitry in a run state and to bleed or drain energy from energy storage devices in a sleep state. In some embodiments, the power control circuit may leave the battery voltage connected to some circuitry, provided that the current drain is not too great for long periods of storage (e.g. several months to years). However, the power control circuit 200 should drain the energy from the busses/capacitors such that the total energy stored in the circuitry is less than a level that could ignite any sterilizing gas.

From the foregoing, it will be appreciated that specific embodiments of the disclosed technology have been described herein for purposes of illustration, but that various modifications may be made without deviating from the technology. For example, bi-stable switch configurations other than a JK flip flop could be used including D-type flip flops, RS-type flip flops or other logic configurations that are configured to retain a state until directed to change states and that draw little power. In general, any bi-stable switch configuration with the following features could be used: 1) the bi-stable switch state is maintained with a very small amount of power such that the battery is not unduly depleted in long-term storage; 2) the bi-stable switch reliably powers up in a known state, either on or off, when the battery is replaced; 3) the bi-stable switch is tolerant of EMF interference such that it cannot easily be switched by such fields. Any of these switch features might be relaxed in embodiments that do not require them. In addition, the disclosed embodiments can be used with circuitry other than implantable circuitry for treating pain with electrical pulses. For example, the disclosed embodiments can be used with implantable cardiac pacemakers or defibrillators or other implantable or non-implantable electronic devices that require sterilization before use and that store sufficient energy that could ignite a flammable sterilizing gas. Other uses for the disclosed technology include use in treating acute or episodic conditions with neuro-stimulators. These devices require leads that pierce the skin and are generally implanted under sterile conditions. A sterile stimulator with the disclosed power control circuit can make installation and testing of these leads more convenient for the patient and physician.

In some embodiments, the disclosed technology can be used with devices that are to be placed in a sleep state and de-powered to a safe handling level without the need to be placed in an explosive sterilizing environment. For example, circuitry for high voltage power supplies such as the type used in X-ray imaging equipment, ultrasound imaging, MRI devices, cathode ray displays or other vacuum tube-based designs or other devices that produce voltage levels that are potentially dangerous if touched or if they arc. Other representative non-medical devices that can be powered down in a sleep state include circuits for use in rockets or other devices that are sometimes exposed to flammable environments during use or storage. The disclosed circuitry can be used to place such devices in a sleep state until they are to be awakened in an environment where the presence of higher voltages is not dangerous.

Certain aspects of the technology described in the context of particular embodiments may be combined or eliminated in other embodiments. For example, the embodiments described above can be produced without a battery and the battery supplied by an end user prior to sterilization and storage. Further, while advantages associated with certain embodiments of the disclosed technology have been described in the context of those embodiments, other embodiments may also exhibit such advantages, and not all embodiments need necessarily exhibit such advantages to fall within the scope of the present technology. Accordingly, the disclosure and associated technology can encompass other embodiments not expressly shown or described herein. 

I claim:
 1. A power control circuit for use with a device having circuitry that is configured to be powered by a power source and that can be placed in a flammable sterilizing gas before use, the power control circuit comprising: a bi-stable switch connectable to the power source and configured to produce an output to put the circuitry of the device in a run state or a sleep state; and one or more transistors that are connectable to one or more energy storage devices in the circuitry of the device and that are controlled by the output of the bi-stable switch to drain stored energy from the one or more energy storage devices to a level below an ignition level of the sterilizing gas when the output of the bi-stable switch is set to put the circuitry of the device in the sleep state.
 2. The power control circuit of claim 1, wherein the bi-stable switch is a flip flop with an output that is connected to the one or more transistors to drain energy from the one or more energy storage devices when the flip flop produces an output to put the circuitry of the device in the sleep state.
 3. The power control circuit of claim 2, further comprising a capacitor connected between the power source and a transistor of the flip flop such that upon application of power from the power source to the flip flop, the power turns on the transistor and produces the output that causes the circuitry of the device to operate in the run state.
 4. The power control circuit of claim 2, wherein the flip flop comprises a pair of cross-connected transistors and wherein each cross-connected transistor of the flip flop is connected in series with a resistance to limit current flow through the cross-connected transistor while the cross-connected transistor of the flip flop is conducting.
 5. The power control circuit of claim 1, further comprising a transistor positioned between the power source and the circuitry of the device, wherein the output of the bi-stable switch controls the transistor to selectively connect the power source to the circuitry when the output of the bi-stable switch puts the circuitry in the run state.
 6. The power control circuit of claim 1, further comprising a remotely actuatable switch that is actuatable through a packaging to change the state of the bi-stable switch and produce an output to place the circuitry of the device in the run state.
 7. The power control circuit of claim 6, wherein the remotely actuatable switch is a magnetically actuated switch.
 8. The power control circuit of claim 7, wherein the remotely actuatable switch is a magnetically activated reed switch.
 9. The power control circuit of claim 6, wherein the remotely actuatable switch is controllable by light.
 10. The power control circuit of claim 6, wherein the remotely actuatable switch is controllable with a shock.
 11. The power control circuit of claim 6, wherein the remotely actuatable switch is pressure activated.
 12. A trial stimulator for applying therapeutic pulses to a patient that can be placed in a permeable package and sterilized with a flammable sterilizing gas; the trial stimulator comprising: a power source; circuitry, including one or more capacitors, that is selectively connected to the power source to produce the therapeutic pulses; a bi-stable switch that is connected to the power source and that is configured to produce an output to put the circuitry of the trial stimulator in a run state or a sleep state; and one or more transistors that are controllable by the output of the bi-stable switch such that when the bi-stable switch produces an output to put the circuitry in the sleep state, one transistor disconnects the circuitry from the power source and another transistor drains energy from the capacitors to a level that is below an ignition level for the flammable sterilizing gas.
 13. The trial stimulator of claim 12, further comprising a remotely actuatable switch that is activatable through the permeable package to change the state of the bi-stable switch to produce an output that puts the circuitry in the run state.
 14. The trial stimulator of claim 13, wherein the remotely actuatable switch is a magnetic reed switch that is activatable via a magnet from outside of the permeable package.
 15. The trial stimulator of claim 12, wherein the bi-stable switch is configured to produce an output to put the circuitry in the run state when power is first applied to the bi-stable switch.
 16. The trial stimulator of claim 12, wherein the bi-stable switch is a flip flop circuit having cross-connected transistors.
 17. The trial stimulator of claim 16, wherein the cross-connected transistors of the flip flop circuit are each connected in series with a resistor to limit current passed by the cross-connected transistor when the cross-connected transistor is conducting.
 18. The trial stimulator of claim 17, further comprising a capacitor connected between the power source and a gate of the cross-connected transistor of the flip flop circuit to cause the flip flop circuit to produce the output that puts the circuitry in the run state when power is first applied to the flip flop circuit.
 19. The trial stimulator of claim 16, wherein the cross-connected transistors of the flip flop each include a gate electrode and a capacitor connected between the gates and a reference voltage or ground to shunt electromotive force (EMF) signals.
 20. The trial stimulator of claim 12, wherein the permeable package includes a gas permeable material that is permeable to the sterilizing gas but is impermeable to microbes.
 21. A power control circuit for use with a connected device having circuitry that can be placed in a permeable package and exposed to a flammable sterilizing gas before use, the power control circuit comprising: a battery; a flip flop circuit, having a pair of cross-connected transistors, and that is configured to produce an output to put the circuitry of the connected device in a run state or a sleep state; one or more transistors that are connected to one or more energy storage devices in the circuitry of the connected device and that are controlled by an output of the flip flop circuit to drain stored energy from the one or more energy storage devices to a level that is below an ignition level of the sterilizing gas when the output of the flip flop produces an output to put the circuitry of the connected device in the sleep state; and a remotely actuatable switch that is configured to be actuated from outside of the permeable package to cause the flip flop to produce the output that puts the circuitry of the connected device in the run state without removing the power control circuit from the permeable package. 